The production of metals such as iron, nickel, copper, aluminum, lead, cobalt and platinum is typically done through smelting the concentrated ores in several smelting and purification processes. Impure and low ore pellets that are introduced into the pyrometallurgical furnace are commonly referred to as concentrates. Ore contained within the concentrates is often oxidized and mixed with silicates, other metals and other impurities. When the concentrates are exposed to high temperatures during smelting, these impurities are separated from the desired molten metallic phase and can be removed by tapping or by other techniques.
The desired molten metallic phase is known as the metal or matte phase while the impurities form a slag phase. The density of the matte phase is generally higher than the slag phase. This difference in density allows for the separation of the slag and matte phases as the slag tends to float atop the molten matte phase. The boundary between the molten matte phase and the slag is commonly referred to as the matte/slag interface.
From both a production and economic point of view it is desirable to determine the location of the matte/slag interface level. The speed and economy of production is affected by accurate knowledge of matte and slag volumes and levels in a furnace as the decision to tap the slag and matte is based on the levels of each phase within the furnace. Reliable and accurate measurement of the matte/slag interface level contributes to better overall control of the smelting process. Moreover, knowledge of the interface level is important for the structural integrity of the furnace and contributes to the design process.
Currently, several techniques are available to measure the levels of the matte and slag phases in a furnace. These techniques include the use of sounding bars, bath level predictors and microwave sensors.
Using a sounding bar is a well known technique and involves dipping a steel rod directly into the furnace bath. Differences in the way the matte and slag phases react with the rod are used to estimate the position of the slag/matte interface. This technique suffers from accuracy and repeatability problems and is prone to human error.
A bath level predictor uses process information such as feed rate, metal production and tapping information to estimate the levels within the furnace based on a mathematical algorithm. This is an indirect measurement and depends on accurate process information as well as regular calibration.
Another known method uses a microwave system to estimate the thickness of the slag phase using a transmitter and receiver located on the roof, or top surface, of the furnace. Microwave signals are transmitted from above and reflected from the slag phase and the matte phase. In practice however, the high conductivity of the slag phase prevents effective penetration of the microwave signals to the slag/matte interface from above. Microwave signals returned to the detector from the slag/matte interface tend to be significantly attenuated and as a result, accurate measurements of the level of the interface are difficult to achieve.